The energy requirement of mobile terminals has increased continuously in recent years. This increase is attributed to an enhanced functionality of the mobile terminals and a greater processing power of the processors integrated therein. Owing to the increased energy requirement, rechargeable batteries are required which have a high charge storage capacity to enable a long operating time of the mobile terminals. Lithium-ion batteries, for example, have hitherto been used for this purpose.
Mobile terminals are often exposed to high ambient temperatures, particularly when used in a motor vehicle. However, high ambient temperatures are damaging to the rechargeable batteries of the mobile terminals. Resultant effects are, for example, instabilities in the output voltage and a reduction in the charge storage capacity. With this, the rechargeable batteries exhibit greater sensitivity to high ambient temperatures when they are fully charged.
To reduce the described impairment of the rechargeable battery at high ambient temperatures, it is proposed that the charge status of the rechargeable battery be limited to a fixed percentage (e.g. 75%) of the charge storage capacity. However, this means that the charge storage capacity cannot be fully utilised generally, i.e. also in the case of a low ambient temperature.
As an alternative to fixing the limit of the charge status of the rechargeable battery, European patent application EP 2 061 129 A1 describes a special discharge circuit. The discharge circuit forms an additional hardware component, which is integrated in the housing of a lithium-ion battery. Under certain criteria, such as when a critical ambient temperature is reached, the lithium-ion battery is automatically discharged up to a predetermined charge status. The discharge and the associated generation of heat take place here in the immediate vicinity of the cells of the rechargeable battery.
Similar principles are described in US patent applications US 2004/0167741 A1 and U.S. Pat. No. 6,222,346 B1, which provide circuits for regulating or limiting the charge status of a rechargeable battery according to temperature.